The recent literature contains many disclosures of mercaptoacyl amino acids that inhibit the action of angiotensin converting enzyme in mammals and that are useful for the treatment of hypertension. One such reference is U.S. Pat. No. 4,211,786, issued July 8, 1980. This patent discloses compounds having the formula ##STR4## and basic salts thereof, wherein: R.sub.f is hydrogen, alkyl, aryl, arylalkyl or ##STR5## wherein R.sub.j is alkyl or aryl; R.sub.g is hydrogen or alkyl; R.sub.h is aryl; R.sub.i is hydrogen, alkyl or arylalkyl; and n is 0, 1 or 2.
A second reference is Belgian Pat. No. 879,158. This patent discloses compounds having the formula ##STR6## and salts thereof, wherein R.sub.g is hydrogen or alkyl and X is methylene or sulfur.